Both primary, lead-acid, and secondary, nickel-zinc for example, batteries contain separators. The primary function of the separator is to keep the positive and negative cell components apart, preventing electronic shorts but not inhibiting ionic transport in the cell. In both applications the separators must be chemically and mechanically stable, and have long life expectancy, the requirement being more stringent in secondary batteries.
In nickel-zinc batteries, the cycle life is related to a substantial degree to separator properties, and the literature reports that batteries made with separators having low electrolytic resistivity have the longest life cycle. In these batteries the separators must have good physical and chemical stability including resistance to concentrated alkali. Types of separators used by those skilled in the art include fibrous and membrane separators, the first type being represented by non-woven polypropylene and nylon webs, and asbestos mats or inorganic filled polymeric non-woven materials. Permeable membranes include porous sheet separators as polyethylene, Dynel, polypropylene and the like. Semipermeable separators are represented by cellulose films, modified methylcellulose, cellophane and the like. Synthetic membranes include polyethylene grafted membranes and ion exchange membranes. A synthetic polymeric membrane separator is described in U.S. Pat. No. 3,629,161, prepared by first making 6,6-Ionene by reacting N,N,N',N'-tetramethylhexanediamine with 1,6-dibromohexane, dissolving polyvinyl alcohol in water, reacting tetrachloro-o-benzoquinone and the 6,6-Ionene, reacting, and casting films from the reaction product. Improved polymeric membranes are a continual objective, especially for use in secondary battery applications.